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Hybrid organic–inorganic perovskite (HOIP) ferroelectrics with high Curie temperature (Tc), typified by the lead halide hybrid perovskite ferroelectrics, are developing rapidly owing to their maneuverable ferroelectricity at high temperatures. However, acquiring high‐Tc lead‐free HOIP ferroelectrics via rational strategy still needs development. In this study, a brand‐new program by modulating the steric confinement in a cuplike cavity to design high‐Tc bismuth‐halide ferroelectrics [H2mdap]BiX5 (H2mdap = N‐Methyl‐1,3‐Propanediamine, X = Cl (1), Br (2), I(3)) is proposed. Emphatically, the Tc enhanced dramatically from 264 K of 3 to 318 K of 2 and 377 K of 1, induced by the substitution of Br and Cl to I, accompanied with an interesting transition from second‐order phase transition (for 3) to the first‐order one (for 1 and 2). The extent of Tc increase is up to 113 K, which far outweighs that of reported Pb‐halide hybrid ferroelectrics. Structural and computational analyses elucidate that this unprecedented improvement of Tc is due to the higher phase transition energy barriers induced by modulating the steric confinement of cuplike cavity via halogen substitution. These results will provide new inspiration for designing high‐Tc lead‐free HOIP ferroelectrics. [ABSTRACT FROM AUTHOR]

Halide hybrid perovskites are attracting considerable attention as highly promising candidates for directly sensing X‐ray radiation, but it is challenging to realize passive X‐ray detection without an external power supply. However, the bulk photovoltaic effect (BPVE) in ferroelectrics promotes the independent separation of photoexcited carriers. Herein, by dimensionality reconstruction of a pure‐two‐dimensional (P‐2D) monolayered perovskite (CH3OC3H9N)2PbBr4, we obtained a quasi‐two‐dimensional (Q‐2D) ferroelectric (CH3OC3H9N)2CsPb2Br7. Converting P‐2D into Q‐2D perovskite stimulates a significant BPVE associated with robust ferroelectricity, as well as an enhanced mobility lifetime product. These features show the potential of the first passive X‐ray detector based on ferroelectrics with an impressive sensitivity up to 410 μC Gy−1 cm−2 at zero bias, which is even superior to the value of the state‐of‐the‐art α‐Se detector operated at relatively high bias. [ABSTRACT FROM AUTHOR]

Polarized light detection is attracting increasing attention for its wide applications ranging from optical switches to high‐resolution photodetectors. Two‐dimensional (2D) hybrid perovskite‐type ferroelectrics combining inherent light polarization dependence of bulk photovoltaic effect (BPVE) with excellent semiconducting performance present significant possibilities. Now, the BPVE‐driven highly sensitive polarized light detection in a 2D trilayered hybrid perovskite ferroelectric, (allyammonium)2(ethylammonium)2Pb3Br10 (1), is presented. It shows a superior BPVE with near‐band gap photovoltage of ca. 2.5 V and high on/off switching ratio of current (ca. 104). Driven by the superior BPVE, 1 exhibits highly sensitive polarized light detection with a polarization ratio as high as ca. 15, which is far more beyond than those of structural anisotropy‐based monocomponent devices. This is the first realization of BPVE‐driven polarized light detection in hybrid perovskite ferroelectrics. [ABSTRACT FROM AUTHOR]

Photosensitive organic–inorganic hybrid ferroelectrics are emerging as a new class of promising materials with a broad spectral response (e.g. visible light, UV light, and IR light) for optoelectronic applications. However, spectrally customized photoresponses in ferroelectrics have not been achieved. Herein, we report a photosensitive organic–inorganic hybrid ferroelectric, (diisobutylammonium)3ClCoCl4 (1), with a notable spontaneous polarization of approximately 4.6 μC cm−2 and high Curie temperature (Tc=372.5 K). More interestingly, it features spectrally selective absorption at specific wave bands ranging from 550 to 700 nm with a large absorption coefficient, which was assigned to the d–d transition of Co2+ from the 4A2 to the 4T1 (P) state. It is emphasized that 1 shows spectrally customized photosensitivity with distinct photocurrent generation under light illumination at 550–700 nm. This is the first hybrid photosensitive ferroelectric with a spectrally customized photoresponse. This finding should lead to innovative applications of hybrid photosensitive ferroelectrics, especially towards spectrally selective optoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: Cesium‐lead halide perovskites (e.g. CsPbBr3) have gained attention because of their rich physical properties, but their bulk ferroelectricity remains unexplored. Herein, by alloying flexible organic cations into the cubic CsPbBr3, we design the first cesium‐based two‐dimensional (2D) perovskite ferroelectric material with both inorganic alkali metal and organic cations, (C4H9NH3)2CsPb2Br7 (1). Strikingly, 1 shows a high Curie temperature (Tc=412 K) above that of BaTiO3 (ca. 393 K) and notable spontaneous polarization (ca. 4.2 μC cm−2), triggered by not only the ordering of organic cations but also atomic displacement of inorganic Cs+ ions. To our knowledge, such a 2D bilayered Cs+‐based metal–halide perovskite ferroelectric material with inorganic and organic cations is unprecedented. 1 also shows photoelectric semiconducting behavior with large “on/off” ratios of photoconductivity (>103). [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) layered hybrid perovskites have shown great potential in optoelectronics, owing to their unique physical attributes. However, 2D hybrid perovskite ferroelectrics remain rare. The first hybrid ferroelectric with unusual 2D multilayered perovskite framework, (C4H9NH3)2(CH3NH3)2Pb3Br10 ( 1), has been constructed by tailored alloying of the mixed organic cations into 3D prototype of CH3NH3PbBr3. Ferroelectricity is created through molecular reorientation and synergic ordering of organic moieties, which are unprecedented for the known 2D multilayered hybrid perovskites. Single-crystal photodetectors of 1 exhibit fascinating performances, including extremely low dark currents (ca. 10−12 A), large on/off current ratios (ca. 2.5×103), and very fast response rate (ca. 150 μs). These merits are superior to integrated detectors of other 2D perovskites, and compete with the most active CH3NH3PbI3. [ABSTRACT FROM AUTHOR]

Perovskite ferroelectrics with prominent nonlinear optical absorption have attracted great attention in the field of photonics. However, they are traditionally dominated by inorganic oxides and exhibit relatively small nonlinear optical absorption coefficients, which hinder their further applications. Herein, we report a new organic--inorganic hybrid bilayered perovskite ferroelectric, (C4H9NH3)2(NH2CHNH2)Pb2Br7 (1), showing an above-room-temperature Curie temperature (~322 K) and notable spontaneous polarization (~3.8 μC cm--2). Significantly, the unique quantum-well structure of 1 results in intriguing two-photon absorption properties with a giant nonlinear optical absorption coefficient as high as 5.76 X 103 cm GW--1, which is almost two-orders of magnitude larger than those of mostly traditional all-inorganic perovskite ferroelectrics. To our best knowledge, 1 is the first example of hybrid ferroelectrics with giant two-photon absorption coefficient. The mechanisms for ferroelectric and two-photon absorption are revealed. This work will shed light on the design of new ferroelectrics with two-photon absorption and promote their potentials in the photonic application. [ABSTRACT FROM AUTHOR]

Highlycontrollable photoelectric switches are urgently demandedin the field of nonlinear optics. In the present work, high-performancequadratic molecular nonlinear optical (NLO)-switches based on organichydrogen-bonded ferroelectric materials, showing large contrasts (upto ∼68%), tunable reversibility, and superior switching “on–off”time, were first prepared from the highly oriented thin polymer films,which overcome the stability problems of the conventional photochromiccounterparts and throw light on the further research of NLO-switchingmaterials from the emerging field of organic molecular ferroelectrics. [ABSTRACT FROM AUTHOR]

Abstract: Bis(imidazolium) l-tartrate crystals (1) were obtained as the molecular ferroelectric materials, which undergoes an above room-temperature reversible phase transition with a symmetry breaking of 222F2 around 359.7 K. A typical Debye-type dielectric relaxation was investigated during the transition process. The variable–temperature structure determination reveals that 1 belongs to the orthorhombic system with a nonpolar space group of P212121 in its paraelectric phase, while the re-determined crystal structure at room temperature is monoclinic with the polar space group of P21, being confirmed by the existence of piezoelectric coefficient d 22 (~6.5 pC/N), the pyroelectric currents and the ferroelectricity. All the experimental findings indicate that 1 should be an above room-temperature molecular ferroelectric material with the highest phase transition temperature than other ferroelectrics in the tartrate family. [Copyright &y& Elsevier]